This invention relates to the preparation of polyurethane-backed substrates, particularly textiles backed with a cellular polyurethane backing.
Polyurethane-backed textiles are well known and described, for example, in U.S. Pat. Nos. 3,821,130, 3,862,879, 3296,159, 4,657,790, and 4,696,849. There are two general types of polyurethane backings commonly used. One type is a substantially non-cellular backing which is normally coated onto the back of tufted textiles to bind the individual tufts of facing yarn to a primary scrim or grid. Such backings are often referred to as "unitary" backings. The other important type is a cellular backing which is attached to a textile to provide an attached cushion. In the carpet area, this type of backing often eliminates the need to install a separate padding material.
It is often desirable to apply multiple layers of the polyurethane. This is particularly true in preparing textiles with a cellular polyurethane backing. In preparing these textiles, it is preferred to apply a substantially non-cellular polyurethane directly to the back of the textile, and then overcoat this "precoat" with a cellular polyurethane layer. The precoat layer helps bind the facing material to the textile and provides a smoother surface on which to apply the cellular layer. This in turn helps to prepare a cellular layer of uniform gauge, which is of particular importance.
In order for the textile to have optimal properties, it is necessary that the bonding between the textile and the various layers be as strong as possible. Unfortunately, quite often a line of bubbles develops at the interface between successive polyurethane layers, especially between the layers of non-cellular polyurethane and cellular polyurethane. The bubble line weakens the bond between the layers to the point that they can often be easily peeled apart. When installed, forces applied to the exposed surface of the textile can cause a separation of the layers when such a bubble line is present. In addition, the presence of the bubble line is cosmetically unacceptable.
Accordingly, it is desirable to prepare a polyurethane-backed textile wherein the bubble line between successive polyurethane layers is minimized or eliminated.